The present invention relates to a novel shotgun cartridge adapter that enables safe firing of subcaliber rim-fire shot cartridges in a standard shotgun.
Small-caliber, low-power shot pellet charges have always been useful for various sporting purposes as well as for elimination of small pests. Their relatively short range and limited power make them safe to use in circumstances where bullet charges would be prohibitively dangerous. For example, small-caliber, shot charges allow for use in confined areas and populated areas. This makes the ammunition especially desirable for shooting birds or other small game, or for target shooting and training young shooters.
A major advantage of the small (typically, .22 caliber) rim-fire, shot cartridge is its substantially lower cost compared to virtually all other larger caliber, more powerful types of ammunition. However, a major disadvantage is its effective use requires a non-rifled, smooth-bored firearm. Unfortunately, such smooth-bored weapons are not commonly available and tend to be prohibitively expensive.
Consequently, prior attempts have been made to develop an adaptive cartridge to allow for the safe use of this ammunition in conventional shotguns. Likewise, attempts have been made to produce adaptive cartridges for use with subcaliber rim-fire bullet cartridges in both rifled firearms and smooth bore shotguns. The primary incentive for development of bullet cartridge adapters is the low cost of the subcaliber ammunition; it makes practice shooting far less expensive. A secondary incentive is the occasional desire to target small game while hunting large game with the same gun.
All of these cartridge adapters, or "inserts", as they are sometimes called, suffer from several significant problems--the most significant of which is an increased danger of accidental discharge.
The safety concern with all cartridge adapters is substantially more significant than the similar concern for ammunition alone. All firearm ammunition present potential hazards and must be treated with care to prevent accidental detonation prior to being loaded in a gun. In the event of accidental detonation, by burning, crushing or occasionally by dropping, all ammunition will explode. Because the shell containing the explosive powder is not contained within a gun's breech and because there is no bore and muzzle to allow for sustained, controlled, rapid, gas expansion behind the shot pellets or bullet, the pellets or bullet will not travel a significant distance with any force. The effect is more like a "firecracker" than a gun. The danger is limited to the immediate proximity of the exploding ammunition.
Cartridge adapters, however, present a much more dangerous situation. For example, see the cartridge adapters presented in U.S. Pat. Nos. 2,352,476 to French; 3,598,053 to Glater; 3,640,013 to Franklin; 4,418,488 to Hughes; and 4,430,940 to Jermunson.
First, since the ammunition is invariably encased within the adapter, a breech is formed, even if the adapter is not inserted within the firearm. Second, many cartridge adapters locate the ammunition toward the rear of the cartridge, providing, in effect, a breech, bore and muzzle within the adaptor itself. Third, all cartridge adapters have substantially greater weight than the ammunition itself. This significantly increases the potential force upon impact to the encased ammunition in the event the loaded cartridge adapter is dropped. Fourth, most cartridge adapters, in order to load the subcaliber ammunition into the cartridge, involve a pressured insertion of a firing pin mechanism upon the ammunition, or a screwing together of two cartridge subparts, one of which contains the ammunition.
Consequently, the likelihood of accidental detonation is dramatically increased. Any debris of prior firings or a foreign body within the cartridge adapter could cause increased pressure upon the ammunition, sufficient for detonation, when the adapter is being loaded or assembled. Dropping the loaded cartridge adapter, because of its total weight, could direct sufficient force for detonation on the exposed surfaoe of the firing pin mechanism. If accidental detonation occurs, because the ammunition is encased within a breech, the shot pellets or bullet will discharge with potentially catastrophic force to the user or anyone nearby.
The two most important factors in enhancing cartridge adapter safety, therefore, are limiting the exposed surface area of the firing pin mechanism and limiting the presence of debris from prior firing, or foreign substances within the cartridge adapter. Both of these factors are complicated by the need to produce a cartridge adapter which directs the detonating force of the "center-fire" firing pin for large-caliber firearms to the rim of the subcaliber "rim-fire" ammunition within the cartridge adapter.
Early designs, such as the aforementioned U.S. Pat. Nos. 2,352,476 to French and 3,640,013 to Franklin, maximized the danger by simply positioning the subcaliber ammunition eccentrically within a normal caliber cartridge. The position was such that the "center-fire" firing pin was aligned with the rim of the subcaliber ammunition. No secondary firing pin mechanism was used and the entire rim area of the subcaliber ammunition was exposed. The result was a very dangerous cartridge adapter, highly susceptible to discharge upon impact, as opposed to assembly. Further, it should be noted that such eccentric positioning of a pellet shot cartridge within a rifled shotgun bore would inherently result in inferior shot-pattern uniformity and inaccuracy due to a skewed pattern center.
Later models, such as U.S. Pat. Nos. 3,598,053 to Glater and 4,418,488 to Hughes, utilizing secondary firing pin mechanisms, attempted to centrally locate the subcaliber ammunition and direct the force of the "center-fire" firing pin to the rim of the subcaliber ammunition. These cartridge adapters typically suffer from a problem related to the secondary firing pin mechanism. The force from the "center-fire" firing pin is usually translated to chisel-pointed forks travelling along channelled cylinders or chisel-pointed cylinders, which impact the rim of the subcaliber ammunition causing detonation. These systems fail to provide sufficient backup for the subcaliber ammunition to adequately preclude rupture of its brass base upon firing. Any rupture of the ammunition's base will subject the firing pin mechanism to blow back of gases and powder residue which could result in subsequent misfires. This also will increase the probability of an inadvertent discharge upon assembly resulting from accumulation of residue and debris.
Some later cartridge adapters have solid base plates through which a secondary firing pin passes to impact the rim; e.g., see U.S. Pat. No. 4,430,940 to Jermunson. However, in order to load these adapters a large firing pin mechanism is pressure inserted behind the subcaliber ammunition. Unfortunately, this creates a substantial risk of an accidental assembly discharge, when a foreign particle becomes lodged between the ammunition's base and the firing pin mechanism.
Further, the width of the removable firing pin mechanism in Jermunson is the same as the width of the subcaliber ammunition. Although the pin itself is narrower, the entire mechanism is in direct contact with the entire rim of the subcaliber ammunition. This, too, greatly enhances the possibility of an impact accidental discharge.
Those cartridge adapters with high degrees of accidental discharge outside the firearms are also extremely dangerous within firearms that utilize an ammunition storage system of individual cartridges stored end to end. This is common in "lever-action" rifles and "pump-action" rifles and shotguns. An impact initiated accidental discharge within the magazine could produce a chain reaction discharge of the forward, normal caliber ammunition with disasterous results.
The danger is even more substantial in "semi-automatic" or "auto-load" firearms. The spring-loaded mechanism, as used in these firearms, must be manually cycled when firing subcaliber ammunition in a cartridge adapter due to the lower than normal firing pressures.
When such a mechanism is released or actuated manually, the high breech closing forces (impacting such an adapter contained cartridge) can be sufficient to cause accidental discharge. This is particularly the case if a slamming bolt face contained contaminate grit and were to impact a firing pin of such a diameter that exceeds that of the firearms' receiver or bolt firing pin clearance diameter.
Those cartridge adapters with secondary firing pin mechanisms, wherein the subcaliber ammunition's base is inadequately supported, have reliability problems resulting from the blowback of explosive gases and debris. This leads to a high number of misfires with prolonged use. Cartridge adapters utilizing firing pin mechanisms, wherein a narrow pin travels laterally from the center to the rim through a narrow tube, have been found to be easily influenced by adverse environmental influences, leading to unpredictable performance.
Although the early, simple cartridge adapters, utilizing only eccentric positioning of the subcaliber rim-fire cartridge, would reliably discharge, the poor accuracy of these adapters produced an unreliable effect of the discharge.
Accordingly, it is the primary objeot of the present invention to provide an improved cartridge adapter which will enable a user to safely discharge subcaliber, rim-fire, shotshells in conventional shotguns.
It is another object to provide a reliable shotshell cartridge adapter which will not misfire unpredictably upon prolonged use.
It is yet another object to provide a shotshell cartridge adapter which improves the effective accuracy of the discharged shot pellets.
It is a still further object to provide a shotshell cartridge adapter, commensurate with the above-listed objects, which is inexpensive to manufacture and easy to use and maintain.